1. Field of Utilization in Industry
This invention relates to an air filter having a pleated filter member for filtering contaminated air and to a method of producing such an air filter.
2. Prior Art
Conventionally, an air filter having a filter member made of a sheet-like porous material, such as a paper or a non-woven fabric, has been used as means for filtering contaminated air, which is provided in an air cleaner for home use or for an automobile, a vacuum cleaner, and so forth. Generally, an air filter of this kind is equipped with a filter member obtained by folding the sheet-like porous material into a pleat form in order to improve filtering efficiency and service life of the filter member. The pleated filter member is held in a predetermined folded form by independent holding members that are fixed to the edge portions of the filter member generally throughout the full length thereof to realize desired filter effects and to facilitate mounting at a given position or exchanging thereof. The holding members are made of a sheet-like material having a rigidity sufficient to maintain at least its own shape. Commercially available adhesives, doublecoated adhesive tapes, heat-fusible films, etc., have been used as a bonding material for mutually fixing the holding members and the filter member.
When the air filter described above is used in an apparatus that is expected to be used in a high temperature environment, such as an air cleaner for an automobile, the bonding material must have a desired heat resistance. In the case of an air cleaner for an automobile, for example, the bonding material of the air filter must have a heat resistance of not lower than 90.degree. C. If the bonding material is not heat resistant, the bonding material melts under high temperature conditions, so that the filter member and the holding members peel off from one another, consequently the filter member cannot hold a pleat form, losing a desired filtering effect. Commercially available double-coated adhesive tapes, for example, do not have high heat resistance.
On the other hand, in production when the holding members are fixed to the edge portions of the filter member, which are folded into pleat form and cut into a predetermined dimension, through the bonding material, it is generally necessary to support the filter member and the holding members at predetermined positions by jigs. For example, when the bonding material is made of a heat resistant adhesive (such as an epoxy adhesive), jigs have been used for, respectively, supporting the filter member and the holding members. The jigs prevent relative movement between the filter member and the holding members until the adhesive cures.
When a heat-fusible film, generally made of vinyl acetate, polyamide, an ethylene-vinyl acetate copolymer, etc., is used as the bonding material, the holding members are first positioned at the edge portions of the filter member with the heat-fusible film. The holding members and heat-fusible film are then heated under pressure by, e.g., a high temperature metal block from the outer face of the holding members, thereby heating and melting the heat-fusible film fixing the filter member edge portions and the holding members. A heat-fusible film having the desired heat resistance, that is, a melting point not lower than 90.degree. C., is not generally tacky. Therefore it is necessary to position and fixedly support the flexible heat-fusible film by jigs at predetermined positions along the edge portions of the filter member, which is also maintained in the pleated form by a jig unless it can maintain its own shape under deformation. The film is then clamped between the holding members, which are supported by another jig, and the filter member, followed by heating under pressure. When the heat-fusible film is heated, the temperature and the heating time must be accurately controlled so that the melted film does not flow out.
As described above, problems arise when an air filter is produced using a heat resistant bonding material. Workability deteriorates significantly due to the use of jigs for supporting the holding members and the heat-fusible film. The working time is also increased.
The object of the present invention is to provide an air filter which can obtain a desired filtering effect, due to the filter member being maintained in a pleated form by holding members which do not peel apart even under a high temperature environment, not lower than 90.degree. C., which air filter can be produced quickly and easily without using jigs for fixing and supporting the holding members during the production process.
It is another object of the present invention to provide a method of producing such an air filter.